If partners discuss contraception — as opposed to the boy simply assuming that the girl is taking care of it — they are more likely to adhere to it. Guys, ask your partner what form of birth control she is using, and also take responsibility by using a condom, the first contraceptive method on our list. As for same-sex sex, contraceptives aren’t necessary, but disease prevention (condoms) are a must.

Condoms: They reduce the risk of STIs (Sexually Transmitted Infections) but are only 85 percent safe in terms of reducing the risk of pregnancy. If a condom does not break and is used 100 percent of the time, it is 100 percent effective. The problem is not with the condom, but with the consistency of using the condom. Occasionally they tear; more often, they are not used correctly. So we recommend that couples having heterosexual sex use dual protection: a condom and one other method of contraception. This ensures that both male and female take responsibility for preventing pregnancy and STIs. For those with a latex allergy, try polyurethane condoms; they may break slightly more easily but they are just as safe against STIs as latex condoms.

The Pill: The Pill, which controls pregnancy by suppressing ovulation, so no egg is out there to meet a sperm, has the longest track record for safety and effectiveness. Taken once a day, most brands result in a menstrual “period” once a month (not a real period because you haven’t ovulated — just a couple of days of light bleeding). The newest brands, Seasonale and Seasonique, were created to get women on an every-three-month menstrual cycle, which is great for gals who find bleeding a bother, are borderline anemic, get really bad cramps or migraines, or are swimmers or athletes for whom periods are an inconvenience that might impact performance. While it’s all right to go long stretches without bleeding if you’re on a pill that suppresses ovulation, it’s not safe to get natural periods less than once every three months; if this is happening, see your doctor.

Spermicidal jelly, foam: Made of nonoxynyl-9 or other sperm-killing agents, these can be inserted into the vagina like a tampon, but unlike a tampon, they do not need to be removed, since the foam or jelly gets absorbed within one to two hours after use. These methods need to be used in conjunction with a condom for pregnancy prevention, not just applied on a condom. Condoms lubricated with spermicidals are still only 85 percent effective against pregnancy; you still need a second form of protection.

Vaginal contraceptive film (VCF):Made of nonoxynyl-9, the active ingredient that kills sperm on contact, VCF can get inserted into the vagina ten minutes before sex. It dissolves to foam, and VCF plus a condom provides close to 100 percent protection against pregnancy.

Medroxyprogesterone (Depo-Provera): A shot given into a muscle (intramuscularly) every twelve weeks that suppresses the release of eggs from the ovaries, thickens cervical mucus to prevent sperm from reaching the egg in the first place, and slows movement of eggs through the fallopian tubes. The main downside is that your appetite will increase, and that can lead to weight gain. Another adverse effect is potential loss of bone density, which is reversible once you stop Depo.

NuvaRing: This is a vaginal ring that you insert within six days of the start of a period, leave in for three weeks, then remove. Another one is then inserted seven days later. It secretes the hormones estrogen and progestin, a synthetic version of progesterone, both of which prevent the ovary from releasing any eggs and thicken cervical mucus. Some girls using NuvaRing develop bacterial vaginosis: a slight change in the normal bacteria that live in the vagina. Symptoms include a funny smell. Bacterial vaginosis is easily treatable with an oral antibiotic or intravaginal cream that your doc can prescribe.

IUD (intrauterine device) or IUS (intrauterine system): IUDs are small, T-shaped plastic devices that are inserted into the uterus for long-term birth control. They come in two forms, one that releases hormones (acting just like the NuvaRing to suppress ovulation) that last for five years (Mirena) and one that contains a small amount of copper and lasts for twelve years (ParaGard). Both interfere with the uterine lining, making it an inhospitable place for a baby to grow. The one with hormones does more to actively prevent conception from taking place by keeping sperm from the egg, just like the Pill, Depo-Provera, and the NuvaRing. IUDs are nearly 100 percent effective at preventing pregnancy but, like all hormonal contraceptives, do not prevent STI, so you’ll need to use a condom as well.